Telomeres

Recently , a number of biotech companies have introduced products containing concentrated Telomerase - the claimed enzyme to telomeres . These products claim to be rejuvinating since they lengthen the cell's telomeres thus promoting the cell's longevity . Since an enzyme ( like a catalyst ) does not become part of the final product but is left to repeat the process over-and-over again. So at what point does the enzyme become ineffective - what is the enzyme's lifespan measurement criteria ? If there is such a criteria - what is it in the case of telomerase . Your assistance in this matter is appreciated .